Modified zn2sio4 compositions



United States Patent 3,329,629 MODIFIED Zn Si COMPOSITIONS Virgil D. Mochel, Corning, N.Y., assignor to Corning Glass Works, Corning, N.Y., a corporation of New York No Drawing. Filed Oct. 30, 1964, Ser. No. 407,889 9 Claims. (Cl. 252-518) ABSTRACT OF THE DISCLOSURE An electrical semiconducting fused ceramic formed by the addition to zinc orthosilicate of minor amounts of the oxides of indium, gallium or zirconium.

This invention relates to electrically semiconducting fused ceramics. In particular it relates to such semiconducting ceramics prepared from modified zinc orthosilicate compositions.

I have now found that the addition of minor amounts of an oxide of indium, gallium or zirconium to zinc orthosilicate results in the formation of a novel ceramic material which is electrically semiconducting. Such materials may be used in the manufacture of resistance elements for electrical applications.

The novel materials of the present invention are fused ceramics consisting essentially of, as analyzed on an oxide basis, Zn SiO and between about 0.5% and 25% by weight, based on the Zn SiO of an activator selected from the group consisting of In O Ga O and Zr0 The phrase fused ceramic as used herein is intended to denote a ceramic material which has been crystallized from a molten state. The semiconductive fused ceramics of the present invention are prepared by crystallization of a molten mixture of Zn SiO and the activator. In one method of preparation, Zn SiO is intimately mixed with an appropriate amount of the activating oxide and the mixture heated to a temperature above 1509 C. The resultant molten mass is then crystallized by cooling. A convenient source of Zn SiO which may be employed is the mineral willemite, a naturally occurring form of zinc orthosilicate.

Alternatively, the activated Zn SiO may be prepared as the reaction product of ZnO and SiO with the activator being incorporated in the reaction mixture. P-referably this is achieved by intimately mixing 56 to 80 parts by weight Zn-O, 44 to 20 parts SiO and an activator oxide in an amount equal to 0.5 to 25 parts by weight per 100 parts of the Zn SiO formed, heating the mixture to a temperature in excess of 1509" C. to form a molten mass of Zn Si'O and cooling the reaction mixture to a crystalline solid. The ZnO and SiO may be employed in the stoichiometric ratio of 73 parts by weight ZnO to 27 parts SiO or either of the two constituents may be present in excess within the limits stated above. How ever, it should be noted that if ZnO is present in excess, the uncombined ZnO in the final composition be activated by the same activators and will constitute a second electrically conductive phase.

In the compositions described herein, the batch constituents have been shown in the oxide form. However, it will be understood that other materials may be substituted which will yield the desired oxides under reaction conditions. For example ZnCO may be substituted for ZnO and In(OH) may be substituted for In O Although I do not wish to be limited to any particular theory as to how the above-described activation takes place, I believe the activation is a result of the incorporation of the activating cation into the lattice structure of the zinc orthosilicate, with the indium, gallium or zirconium ions entering substantially for the zinc. Support for such a theory is found in the fact that X-ray analyses have failed to disclose the presence of the activating oxide as a separate phase.

The following specific examples will serve to further illustrate the present invention in a manner in which it may be practiced:

Example I Zn SiO was prepared by mixing ZnO and SiO in a ratio of about 73:27 at a temperature in excess of 1509" C. and pouring the molten mixture onto a steel slab at room temperature to rapidly crystallize the melt. The resultant crystalline material was probed with an ohmmeter and found to have an infinite resistance. X-ray analysis of the material indicated it to be Zn SiO A portion of the material was then ground and 10% by weight In O was added and mixed. The mixture was melted in a silica crucible at about 1510 C. and cooled by pouring the melt onto an iron slab at room temperature. The resistivity of the resultant product was checked at various temperatures and the following data obtained:

Temp. C.): Specific resistivity (ohm-cm.)

312 Temp. Coefh, percent/ C., 0.23.

Example II Temp. C.): Specific resistivity (ohm cm.) 25 630 Temp. Coeif, percent/ C., 0.12.

Other samples were prepared in a similar manner using varying amounts of In O as well as ZrO and Ga O for the activating oxide. The results indicated that the amount of activating oxide may vary at least between about 0.5% by weight and 25% by weight based on the Zn SiO Furthermore, it was found that while ZrO and 621 0 could be used to activate willemite, their activation ability was considerably less than that of the In O As a result, I prefer to use In O as the activating oxide in the composition of the present invention.

Obviously many modifications and variations of the invention as hereinabove set forth may be made Without departing from the spirit and scope thereof and only such limitations should be applied as indicated in the appended claims.

I claim:

1. An electrically semiconducting fused ceramic consisting essentially of, as analyzed on an oxide basis, Zn Si-O and an activator selected from the group consisting of In O and Ga O said activator being present in an amount of between 0.5 and 25 parts by weight per 100 parts of Zn SiO 2. A fused ceramic according to claim 1 wherein said activator is In O 3. A fused ceramic according to claim 2 wherein said In O is present in the amount of about 10 parts by Weight per 100 parts of said Zn SiO 4. A method of preparing a semiconducting material composed primarily of Zn SiO which comprises (A) forming a mixture of 56 to 80 parts by weight of ZnO, 44 to 20 parts of SiO and an activating oxide in an amount equal to between 0.5 and 25 parts per 100 parts of the Zn SiO subsequently formed, said activating oxide being a member selected from the group consisting of In O Ga O and ZrO (B) heating the mixture to a temperature in excess of about 1509 C. to form a molten mass, and (C) cooling to crystallize the melt.

5. A method according to claim 4 wherein said activating oxides is In 6. A method according to claim 5 wherein said In O is present in the mixture in the amount of about parts per 100 parts by Weight of said Zn SiO 7. A method of preparing a semiconducting material which comprises cooling and crystallizing a molten mass of Zn Si-O containing 0.5 to parts of an activating oxide per parts by weight Zn SiO' said activating oxide being a member selected from the group consisting of 111203, 63.203 and 21 02.

8. A method according to claim 7 wherein said activating oxide is In O 9. A method according to claim 8 wherein said In O is present in said molten mass in the amount of about 10 parts per 100 parts by weight of said Zn SiO References Cited F. A. Kroger; Luminescence of Solids (1948), Elsevier Pub. Co., pp. 287-88.

LEON D. ROSDOL, Primary Examiner.

J. D. WELSH, Assistant Examiner. 

1. AN ELECTRICALLY SEMICONDUCTING FUSED CERAMIC CONSISTING ESSENTIALLY OF, AS ANALYZED ON AN OXIDE BASIS, ZN2SIO4 AND AN ACTIVATOR SELECTED FROM THE GROUP CONSISTING OF IN2O3 AND GA2O3, SAID ACTIVATOR BEING PRESENT IN AN AMOUNT OF BETWEEN 0.5 AND 25 PARTS BY WEIGHT PER 100 PARTS OF ZN2SIO4. 